1. Field of the Invention
The present invention relates to a manufacturing method of a high resistivity silicon single crystal used in a substrate for a radio frequency communication device or the like.
2. Prior Art
In recent years, a demand for a high resistivity substrate has been built up in company with proliferation of a radio frequency communication device used in a short distance wireless LAN. A compound semiconductor technology using GaAs or the like has been conventionally used in more of cases on a substrate of a RF (Radio Frequency) circuit requiring a high resistivity. Such a compound semiconductor substrate, however, has been very expensive.
While a silicon CMOS was thought unsuitable for an RF circuit because of a high power consumption, it has become applicable to an RF circuit due to a great miniaturization and a progress in designing in recent years. Hence, attention has been focussed on a high resistivity silicon wafer excellent in an RF characteristic and economy, such as a mirror finished silicon wafer made from a high resistivity crystal grown with a Czochralski method (CZ method), an SOI (Silicon on Insulator) wafer or the like in place of a substrate made of a compound semiconductor such as GaAs.
A high resistivity silicon wafer can be obtained from a high resistivity silicon single crystal manufactured with a CZ method. In manufacture of a silicon single crystal with a CZ method, the silicon single crystal, as having been well known, is pulled up while being rotated from a silicon melt formed by melting a silicon raw material in a quartz crucible. The silicon raw material is in more of cases poly-silicon rods produced with a Siemens method using especially trichlorosilane as a raw material, which also applies to a case where a high resistivity silicon single crystal is produced without exception.
It has been found that in such a single crystal manufacturing method, however, high resistivity silicon single crystals, in a case where being produced, fluctuate in resistivity around a target value, which trend becomes more conspicuous with an increase in resistivity.
That is, a poly-silicon raw material used in manufacture of a single crystal with a CZ method has been recently of a sufficiently high purity, and while not only is a trace of a dopant added to the high class row material to thereby secure a predetermined resistivity, but a high quality crucible is used and a crucible rotational speed, a pressure in a pulling furnace and the like are also adjusted to thereby obtain a single crystal of a low oxygen concentration, a problem has arisen of a fluctuation in resistivity, which has not been encountered in manufacture of crystals of a common resistivity.